1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to an improvement of such a linear motion rolling contact guide unit excellent in both of dynamic and static stability suitable for use in machining tools, such as heavy cutting tools.
2. Description of the Prior Art
FIG. 4 illustrates a table assembly which may be advantageously used in a machining tool or the like. The illustrated table assembly includes a pair of elongated rails A and B extending in parallel as spaced apart from each other and over a desired distance, four sliders C through F slidably mounted on the rails A and B and a table Y fixedly mounted on the four sliders C through F. The sliders C through F are arranged such that two of them, i.e., C and D or E and F, are slidably mounted on the same rail A or B as spaced apart in a longitudinal direction. Thus, the table Y may move linearly back and forth longitudinally as indicated by a double-sided arrow G.
As shown in FIG. 5, each of the four sliders C through F defines, together with its related rail A or B, a linear motion rolling contact guide unit. In general, a linear motion rolling contact guide unit includes a rail extending over a desired distance, a slider slidably mounted on the rail and a plurality of rolling members interposed between the rail and the slider so as to allow to provide a relative linear motion between the rail and the slider. In the endless type of such a linear motion rolling contact guide unit, the slider is typically comprised of three blocks, i.e., a center block 17 and a pair of end blocks 12 and 13 located at the front and rear ends of the center block.
FIG. 5 illustrates a right half of a transverse cross section of a linear motion rolling contact guide unit defined by rail A and any one of the sliders C and D. In the structure shown in FIG. 5, the rail A is formed with a pair of oppositely inclined inner guide surfaces H and I at each of its opposite sides. The slider C or D has a center block L which includes a horizontal section and a pair of vertical sections Q to thereby define a generally U-shaped cross section. The vertical section A has its inner surface formed with a pair of oppositely inclined outer guide surfaces J and K located spaced apart and opposite to the inclined inner guide surfaces H and J, respectively. Therefore, a load channel is defined between the associated pair of inner and outer guide surfaces H and J or I and K.
The vertical section Q is provided with a pair of endless circulating paths in a crisscross arrangement when viewed in a longitudinal direction as shown in FIG. 5, and the first of the endless circulating paths includes the load channel (or load path section) H and J, a return path section O and a pair of curved connecting path sections S connecting the corresponding ends of the load and return path sections H and J and O. Similarly, the other second endless circulating path includes the load channel (or load path section) I and K, a return path section P and a pair of curved connecting path sections T connecting the corresponding ends of the load and return path sections I and K and P. A plurality of rollers M as rolling members are provided in the first endless circulating path and similarly a plurality of rollers N are provided in the second endless circulating path. In the upper load channels H and J, the rollers M are in rolling contact with both of the inner and outer inclined guide surfaces H and J so that a rolling contact is provided therebetween. In a similar manner, the rollers N are in rolling contact with both of the inclined inner and outer guide surfaces I and K in the lower load channel I and K. Typically, the load and return path sections are provided in the center block and the pair of curved connecting path sections are provided in the front and rear end blocks, respectively.
The linear motion rolling contact guide unit of the structure shown in FIG. 5 has an increased load bearing capacity and provides a smooth sliding motion at high accuracy. The guide unit or the table assembly as shown in FIGS. 4 and 5 are high in stability or rigidity in a static mode, but relatively low in dynamic stability or rigidity. Thus, a problem could arise when it is desired to stop the slider or table accurately at a desired location while carrying a relatively heavy load. Such a problem becomes appreciable when the control of positioning of the slider or table is desired to be carried out on the order of a few microns.
One possible approach to cope with this situation may be the use of balls as rolling members; however, in this case, the stability or rigidity in a static mode becomes degraded. Another approach would be a combination between rollers and a synthetic resin sheet. In this case, however, the durability of the synthetic resin sheet can be a problem and thus this approach only creates a new problem. It is also conceivable to incorporate an additional slider, which serves as a braking element, in combination with the sliders C through F. However, this approach also presents another problem such as increased mass and complication of a manufacturing process.